In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.

What's in a name?

Heptanesia. That was the name Ptolemy, the second-century Greek astronomer and geographer, gave present-day Mumbai. It was an apt name for the seven islands jutting into the Arabian Sea. Centuries later, the local Kolwadi fisherfolk called their villages Mumba, in honor of their patron goddess.

Portuguese explorers, arriving in 1543, named their settlement Bom Bahia—"good bay." The colony was given to King Charles II of England as dowry when he married the Portuguese princess Catherine de Braganza in 1661. A long British presence was established in the emerging city, and the name was anglicized to Bombay. Bombay was the official name for centuries, remaining so even after Indian independence in 1947.

Mumbai is now the official name, established by the Maharashtra state government and its Marathi Hindu leadership in 1995. Harking back to the goddess Mumba, the current name rouses both advocacy and dissension among the city's cosmopolitan population.

And in Dharavi? What do the people of Dharavi call the city in which they live? Dharavi is a diverse enclave, and roots can run deep. Many do call it Mumbai, though it's not unusual to hear Bombay, or even Bombai—somewhere between the two—depending on tradition or family loyalty. Over time, city residents, like the rest of us, are becoming accustomed to saying Mumbai, just as ancient explorers, we imagine, referred to Heptanesia.